samples: bpf: syscall_nrs: use mmap2 if defined

For arm32 xdp sockets mmap2 is preferred, so use it if it's defined.
Declaration of __NR_mmap can be skipped and it breaks build.

Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
Acked-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

samples/bpf/syscall_nrs.c

@@ -9,5 +9,11 @@ void syscall_defines(void)
 	COMMENT("Linux system call numbers.");
 	SYSNR(__NR_write);
 	SYSNR(__NR_read);
+#ifdef __NR_mmap2
+	SYSNR(__NR_mmap2);
+#endif
+#ifdef __NR_mmap
 	SYSNR(__NR_mmap);
+#endif
+
 }